The field of apparatus to install elongate soil sensors is dependant largely on the form of the many types of soil sensors that are available and the type of material or soil into which the sensor is to be placed. The applicant is the inventor and designer of many soil sensors as disclosed in U.S. Pat. No. 5,418,466 entitled “For indicating complex dielectric constant/conductivity of a medium” filed 11 Oct. 1991; AU760525 entitled “Automatic depth sensing detection for portable soil moisture probes” filed 12 Jul. 1999; AU2002331464 entitled “Soil probe insertion arrangement and method of use” filed 4 Oct. 2002; U.S. Pat. No. 7,042,234 entitled “Soil matric potential and salinity measurement apparatus and method of use” filed 16 Dec. 2003; U.S. Pat. No. 7,240,743 entitled “Soil probe insertion arrangement and method of use” filed 4 Oct. 2002, and PCT/AU2014/000383 entitled “Tapered Soil Moisture Sensor Arrangement and Method of Installation” filed 10 Apr. 2014. The information disclosed in all the above mentioned patents and patent applications is incorporated by reference into this specification.
All the sensor housings disclosed in the abovementioned patents and patent application are elongate to permit multiple sensors to be located at various depths in the soil or material to be sensed, and of particular note is that the housings (except PCT/AU2014/000383 and the priority application) are all cylindrical and have a constant diameter along the full inserted length.
The apparatus of the type that is designed to create a cylindrical hole in the ground into which an elongate sensor housing is to be placed is typically referred to as an auger.
An auger is a drilling device, or drill bit, that usually includes a rotating helical screw blade called “flighting” to act as a screw conveyor to remove the drilled out material from the opening as it is being created. The rotation of the screw blade causes the material to be cut and the flighting moves the cut material out of the opening being drilled.
An auger used for digging cylindrical openings in the ground is called an ‘earth auger’, ‘handheld power earth drill’, ‘soil auger’ or ‘mechanised post digger’. This kind of auger can be a manually turned handheld device, and alternatively can be powered by an electric motor or internal-combustion engine, or even attached to a tractor's power take-off.
An auger suitable for the preparation of an opening in the ground suitable for the insertion of a cylindrical soil sensor housing has a construction including; a continuous helical flighting extending from an inserted end along a constant diameter shank to a head end of the shank. Manually operated augers are manipulated using a handle member that extends at right angles to the shank and extends away from the shank a distance long enough for a person to apply a twisting motion to the shank using the handle to turn the auger into the ground and at the same time the user applies a downward pressure to the auger to force the inserted end of the auger into the ground. A sharpened edge on the free end of the flighting at the inserted end or a pre-formed blade fixed to the inserted end of the auger assists the auger to penetrate into the ground.
The referenced sensors (except PCT/AU2014/000383 and the priority application) are all housed in elongate cylindrical housings and the reasons for carefully creating a cylindrical opening in the material, typically the ground, to be sensed include the following:                a. To ensure that the ground in the immediate vicinity of the sensor housing and hence the sensors therein remains as undisturbed as possible.        b. That the physical fitment between the sensor housing and the surrounding ground is such that there is no gap or gaps between the surrounding soil and the outer surface of the elongate soil sensor housing along substantially its full length. Gaps, if they existed, would create the potential for the creation of preferential ground water seepage channels from the surface of the soil, or air gaps, in the immediate vicinity of the sensor which will skew or make unusable the readings of soil moisture and other characteristics of the surrounding soil detected by the sensor/s within the sensor housing.        
These reasons do not become an issue if the gap or gaps are not present but to achieve that outcome using the prior auger arrangements there is a need to ensure that the inner wall of the opening created by the auger is relatively smooth and of constant inner diameter along its full depth. This has been achieved, as described in at least one of the referenced documents, by slightly under-sizing the opening created by the auger relative to the constant outer diameter of the inserted sensor housing, and cutting or slicing away a portion of the inner wall of the prepared opening with the inserted end of the sensor housing adapted to do that slicing as it is inserted into the prepared opening.
It will be noted in the mentioned patent documents that the elimination of a gap or gaps between the sensor housing and surrounding soil is identified as a requirement for the proper operation of the in-situ soil sensor. However, the installation process described in those documents does not ensure that outcome. One problem encountered includes, that any wobbling of the auger by the operator during the creation of the opening can create larger excursions from the sheared volume created when the sensor housing with a cutting arrangement is inserted, such that gaps are left at one or more locations along the length of the inserted sensor housing. If the gap, when air filled is substantial enough or if the gap is occupied by water, the sensor measurements in the gap regions will not be indicative of the soil characteristics in the field of influence of the sensor near or at those gap regions.